Book/Report

FZJ-2018-03869

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Untersuchungen zur physikalischen Zerstäubung an amorphen Kohlenstoffschichten mittels laserinduzierter Fluoreszenz

Pasch, E. (Corresponding author)FZJ*

1992
Forschungszentrum Jülich GmbH Zentralbibliothek Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/19192

Report No.: Juel-2647

Abstract: In order to minimize the radiation losses, it is desirable to keep the plasmas in nuclear fusion devices free of high-Z-impurities. Therefore, the walls of TEXTOR and other tokamaks are covered with thin layers of amorphous carbon layers (a-C:H) or amorphous carbon/boron layers (a-C/B:H). The sputtering behaviour of these layers has been studied under bombardment by Ar$^{+}$ ions with energies of 1.5 keV and current densities of a few mA/cm$^{2}$. Investigations of these coatings were carried out with the object to measure the velocity distribution of the sputtered atoms and the sputtering yields by laser induced fluorescence in thevacuum ultraviolet. Both in order to avoid excessivly high material removal from the films and also to study transient effects, the ion gun was pulsed with 2 Hz repetition frequency for a duration of 30 $\mu$s. To generate the vacuum-UV radiation, two different methods have been applied. The frequency tripling of an excimer laser pumped dye laser in a noble gas mixture has been used in the wavelength ranges of 120.3 - 122.5 nm and 127.0 - 127.9 nm. Continuously tunable radiation down to 120 nm has been produced by a Raman-shifted, frequency doubled dye laser. The energy of thr 9th anti-stokes-line at L$_{\alpha}$ is about 0.1 $\mu$J, the pulse length < 2 ns. The velocity distribution and absolute density of sputtered H (121.6 nm), D (121.5 nm), B (249.8 nm), C (127.8 nm) and O (130.2 nm) have been measured. A Thompson-distribution can be fitted to the experimental points. The best fit gives surface energies of about 1.0 eV for H- or D-, 7.6 for C- and 5.6 for B-atoms. The velocity distribution of atomic oxygen could not be fitted with a single value for the surface energy, but with the superposition of two Thompson-distributions with energies of 0.5 and 4.8 eV. For H-atoms, the sputtering yield shows a strong dependence on the fluence. The effect is considerably stronger for a-C:H than for a-C/B:H layers.

---

Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

---

Database coverage:

---